The present invention relates to an interconnecting system for photovoltaic cells in a power generating module.
Photovoltaic cells are silicon-base crystal wafers which produce a voltage between opposite surfaces when light strikes one of the surfaces, which surface has a current collecting grid thereon. Cells are interconnected into series strips by electrically interconnecting a collector pad on the grid to the opposite surface of the adjacent cell in the strip. Thus a desired voltage may be generated by series interconnecting a predetermined number of cells into a string, and a desired current may be produced by parallel interconnecting the assembled strings. The strings are assembled on a dielectric surface to form a module to facilitate handling and assembly into an array of modules for generating useful amounts of electrical power.
Rectangular wafers are presently undergoing considerable development due to their optimal usage of module area by eliminating the voids between cells of circular and semicircular shape. Further, rectangular cells are more easily manufactured than other shapes since they may be formed by laser cutting a single crystal ribbon. The elongate rectangular cells thus formed are provided with a plurality of side-by-side current collector grids on one surface thereof, and the grids each have a collector pad adjacent one edge of the cell. These are electrically connected to the opposite surface of the adjacent cell in the string by individual leads which are soldered or, more recently, ultrasonically bonded. Soldering of individual connecting leads in the form of wire or foil strips is quite time consuming, which thus adds to the cost of a module. Ultrasonic bonding of foil is more readily adapted to automation, but precludes the possibility of using an insulated connecting lead which would prevent shorting of the lead against the edge of a cell.